Directional coupler

ABSTRACT

A directional coupler includes a laminate including a ground electrode substrate, a dielectric substrate that includes line electrodes thereon, a lead-out conductor substrate that includes lead-out conductors of the line electrodes, a ground electrode substrate, and a protection substrate. External electrodes for grounding, external electrodes for a main line, and external electrodes for a subordinate line are provided in the laminate. The inner line electrode and the outer line electrode preferably have a spiral or helical shape, and the corresponding currents are transmitted in the same direction through sections of these line electrodes that are adjacent and substantially parallel to each other.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to directional couplers, and inparticular, relates to a directional coupler that only couplesmicrowaves that propagate through a transmission line in a firstdirection and obtains an output proportional to the microwave power andthat does not couple microwaves that propagate through the transmissionline in a second direction opposite to the first direction.

2. Description of the Related Art

For example, as described in Japanese Unexamined Patent ApplicationPublication No. 5-160614, waveguide circuits, which have been thepredominant microwave circuits, require high precision machining andthus are not suitable for mass production and are expensive. Moreover, aproblem has existed with waveguide circuits in that the outer dimensionsand weights of the waveguide circuits are large. Thus, microstrips,which can be reduced in size and weight through the use of large-scaleintegration technology have been used in radios, BS receivers, and thelike.

A conventional directional coupler composed of microstrips shown in FIG.6 is disclosed in Japanese Unexamined Patent Application Publication No.5-160614.

This directional coupler is a side-edge type coupler, which has astructure in which sections of respective stripline electrodes 81 a and82 a of microstrips 81 and 82 are disposed close to each other for thelength of λ/4 in the horizontal direction and the upper and lowersurfaces of the microstrips 81 and 82 are covered with ground electrodes83 and 84. In a coupled mode of the sections of the stripline electrodes81 a and 82 a which are disposed close to each other, a first microwavepower is input from a port 1 to the microstrip 81 functioning as a mainline while a second microwave power, that is a fraction of the firstmicrowave power, is generated in a port 3 of the microstrip 82functioning as a subordinate line.

For example, as shown in FIG. 7, in a cellular phone unit, in order tokeep the transmission power at a minimum level through the function ofdividing high frequency signals into two components in theaforementioned directional coupler, a main line 70 a of a directionalcoupler 70 is disposed between a transmission power amplifier 71 and anantenna 72 and one end of a subordinate line 70 b is connected to anautomatic gain control circuit 73 so that the automatic gain controlcircuit 73 adjusts the output of the transmission power amplifier 71.

With regard to cellular phone units and the like, an important issue isto minimize the size. Thus, the size of directional couplers has beenrequired to be further reduced. However, in the directional couplershown in FIG. 6, for example, λ/4 is 7.5 cm (on the condition that thespecific inductive capacity is 1) at 1 GHz. Thus, the required minimumlength of the sections disposed close to each other in the horizontaldirection of the stripline electrodes 81 a and 82 a is 7.5 cm.Accordingly, the size of the substrate, which includes the striplineelectrodes 81 a and 82 a thereon, becomes large. Moreover, for example,when respective substrates that include the ground electrodes 83 and 84thereon are disposed and fastened with screws under and over thesubstrate, which includes the stripline electrodes 81 a and 82 athereon, a problem arises in that a reduction in size is limited and thecost increases.

Accordingly, a directional coupler that is improved to solve theaforementioned problem is proposed in Japanese Unexamined PatentApplication Publication No. 5-160614. In this directional coupler,ground electrode substrates that include ground electrodes thereon arealternately laminated with dielectric substrates on which a pair ofstripline electrodes are provided so that the stripline electrodes aredisposed close and parallel to each other in a spiral shape. Then, thecorresponding stripline electrode components of the individualdielectric substrates are connected in series with each other through apair of via holes that are close to each other so that the striplineelectrodes have the length of a quarter of a wavelength.

In the improved directional coupler, the stripline electrodes having thelength of a quarter of a wavelength are formed with the striplineelectrode components and the via holes so that the stripline electrodesare divided into components on a plurality of laminated dielectricsubstrates. Thus, the size of the improved directional coupler can besmall compared with that of the directional coupler shown in FIG. 6.However, even in the improved directional coupler, the total length ofthe stripline electrodes is required to be a quarter of a wavelength.Thus, the size of the directional coupler cannot be significantlyreduced. Moreover, in general, side-edge type couplers have a problem inthat it is difficult to achieve a high degree of coupling due to thecharacteristics of the distribution of a magnetic field around thestripline electrodes. The improved directional coupler uses side-edgecoupling between a pair of stripline electrodes. Thus, the improveddirectional coupler has a problem in that it is difficult to achieve ahigh degree of coupling.

On the other hand, a directional coupler called a broad-side typecoupler is proposed in Japanese Patent No. 3203253. In this directionalcoupler, spiral-shaped coupled lines are opposed to each other withdielectric layers therebetween so as to achieve coupling between thecoupled lines. Since the inductance value of the coupled lines becomeshigh in the directional coupler, the directional coupler can beconstructed with lines that are shorter than a quarter of a wavelength.Thus, the size can be readily reduced, and a high degree of coupling canbe achieved with a small loss.

However, in the directional coupler disclosed in Japanese Patent No.3203253, since spiral-shaped coupled lines are opposed to each otherwith dielectric layers therebetween so as to achieve coupling betweenthe coupled lines, the capacitance between the coupled lines becomeslarge. Thus, the directional coupler has a problem in that highisolation between the coupled lines cannot be achieved.

Moreover, in the directional couplers disclosed in Japanese UnexaminedPatent Application Publication No. 5-160614 and Japanese Patent No.3203253, coupling is adjusted by adjusting the distance between lines.In this case, a magnetic field and an electric field around the linesare both changed by adjusting the distance between the lines, and it isimpossible to adjust only one of the magnetic field and the electricfield. Thus, it is difficult to adjust isolation. Isolation is aphenomenon in which magnetic field coupling and electric field couplingnullify each other. Thus, isolation has been adjusted only by selectingtypes of materials of substrates on which coupled lines are provided tochange the permittivity and the permeability.

SUMMARY OF THE INVENTION

In order to overcome the problems described above, preferred embodimentsof the present invention provide a small directional coupler that has ahigh coupling value and high isolation characteristics.

In order to achieve this, a directional coupler according to a firstpreferred embodiment of the present invention includes at least onedielectric layer and two line electrodes that are provided on the atleast one dielectric layer. The two line electrodes include an innerline electrode and an outer line electrode that surrounds the inner lineelectrode, as viewed from above. Corresponding currents are transmittedin the same direction through sections of the inner line electrode andthe outer line electrode that are adjacent and parallel to each other.

In the directional coupler according to the first preferred embodimentof the present invention, since the corresponding currents aretransmitted in the same direction through the sections of the inner lineelectrode and the outer line electrode, which are adjacent and parallelto each other, the inductance values of the line electrodes become high.Thus, inductive coupling between the inner line electrode and the outerline electrode becomes strong, and capacitive coupling between the innerline electrode and the outer line electrode becomes weak, therebyachieving high isolation. Moreover, high inductance values can beachieved while the size of the directional coupler is small, and thusthe size of the directional coupler can be reduced. Moreover, theinductance values of the inner line electrode and the outer lineelectrode can be readily adjusted so that the inductance values agreewith each other by adjusting the respective numbers of turns of theinner line electrode and the outer line electrode.

A directional coupler according to a second preferred embodiment of thepresent invention includes at least one dielectric layer and two lineelectrodes that are provided on the at least one dielectric layer. Thetwo line electrodes include a spiral-shaped or helical-shaped inner lineelectrode and a spiral-shaped or helical-shaped outer line electrodethat surrounds the inner line electrode, as viewed from above.

In the directional coupler according to the second preferred embodimentof the present invention, the inner line electrode and the outer lineelectrode are formed so as to have a spiral or helical shape. Thus, thecorresponding currents are transmitted in the same direction through thesections of the inner line electrode and the outer line electrode, whichare adjacent and parallel to each other, and the inductance values ofthe line electrodes become high. Thus, inductive coupling between theinner line electrode and the outer line electrode becomes strong, andcapacitive coupling between the inner line electrode and the outer lineelectrode becomes weak, thereby achieving high isolation. Moreover, highinductance values can be achieved while the size of the directionalcoupler is small, and thus the size of the directional coupler can bereduced. Moreover, the inductance values of the inner line electrode andthe outer line electrode can be readily adjusted so that the inductancevalues agree with each other by adjusting the respective numbers ofturns of the inner line electrode and the outer line electrode.

In the directional couplers according to the first and second preferredembodiments of the present invention, since the degree of inductivecoupling between the inner line electrode and the outer line electrodeis high, the length of each of the inner line electrode and the outerline electrode can be kept to less than a quarter of a wavelength. Thus,the size of the directional coupler can be further reduced.

Moreover, in the directional couplers according to the first and secondpreferred embodiments of the present invention, it is preferable thatthe width of the inner line electrode is smaller than the width of theouter line electrode. When the width of the inner line electrode isreduced, the inductance value of the inner line electrode is increased.Accordingly, even when the number of turns of the inner line electrodeis reduced, the inductance values of the inner line electrode and theouter line electrode can be adjusted so that the inductance values agreewith each other. Thus, the size of the directional coupler can befurther reduced.

Moreover, the number of turns of the inner line electrode may be largerthan the number of turns of the outer line electrode. The inductancevalues of the inner line electrode and the outer line electrode can bereadily adjusted so that the inductance values agree with each other byincreasing the number of turns of the inner line electrode.

Moreover, the inner line electrode and the outer line electrode may beprovided on the same plane. A first area of the spiral-shaped orhelical-shaped outer line electrode opposing the spiral-shaped orhelical-shaped inner line electrode, which first area is located insidethe outer line electrode, is substantially the same as a second area ofthe inner edge of the innermost circumferential of the outer lineelectrode opposing the outer edge of the outermost circumferential ofthe inner line electrode. Thus, only certain sections of the inner lineelectrode oppose sections of the outer line electrode in the first area.Moreover, the thickness of the inner line electrode and the outer lineelectrode is fairly small. Thus, the capacitance between the inner lineelectrode and the outer line electrode is small, and the degree ofisolation between these line electrodes can be significantly increased.

Moreover, the inner line electrode and the outer line electrode may beprovided on different planes. The capacitance between the inner lineelectrode and the outer line electrode can be further reduced byproviding the inner line electrode and the outer line electrode ondifferent planes. Thus, the degree of isolation between these lineelectrodes can be further increased.

Moreover, at least one of the inner line electrode and the outer lineelectrode may be divided into line electrode components that areprovided on a plurality of planes, and the divided line electrodecomponents may be connected in series with each other through a viahole. When the inner line electrode and/or the outer line electrode aredivided into line electrode components that are provided on a pluralityof planes, the number of line electrode components per unit area thatare provided on one plane can be reduced. Thus, the size of thedirectional coupler can be further reduced.

Moreover, the directional coupler according to preferred embodiments ofthe present invention may further include a ground electrode that isprovided on the dielectric layer. Capacitances may be formed between theground electrode and individual ends of the inner line electrode and theouter line electrode. Due to the functions of the capacitances formedbetween the ground electrode and the individual ends of the inner lineelectrode and the outer line electrode, the resonant frequencies of theinner line electrode and the outer line electrode can be reduced. Thus,the size of the directional coupler can be further reduced by shorteningthe lengths of the line electrodes to obtain a predetermined resonantfrequency.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the external appearance of adirectional coupler according to a first preferred embodiment of thepresent invention.

FIG. 2 is an exploded perspective view showing the structure of thedirectional coupler shown in FIG. 1.

FIG. 3 is an exploded perspective view of a directional coupleraccording to a second preferred embodiment of the present invention.

FIG. 4 is an exploded perspective view of a directional coupleraccording to a third preferred embodiment of the present invention.

FIG. 5 is an exploded perspective view of a directional coupleraccording to a fourth preferred embodiment of the present invention.

FIG. 6 shows a conventional directional coupler.

FIG. 7 is a block diagram showing an RF transmitter circuit in which adirectional coupler is used.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Directional couplers according to preferred embodiments of the presentinvention will now be described with reference to the attached drawings.

First Preferred Embodiment

FIGS. 1 and 2 show the external appearance and the exploded structure ofa directional coupler 10 a according to a first preferred embodiment ofthe present invention, respectively. The directional coupler 10 aincludes a chip laminate body 16 including a first ground electrodesubstrate 11, a dielectric substrate 12 that includes an inner lineelectrode 21 a and an outer line electrode 22 a that have a spiral shapeon one major surface thereof, a lead-out conductor substrate 13 thatincludes lead-out conductors 23 a, 24 a, and 25 a of the inner lineelectrode 21 a and the outer line electrode 22 a provided thereon, asecond ground electrode substrate 14, and a protection substrate 15.

External electrodes G for grounding, external electrodes P₁ and P₂ for amain line, and external electrodes P₃ and P₄ for a subordinate line areprovided on side surfaces of the laminate body 16 so as to extend fromthe first ground electrode substrate 11 to the protection substrate 15.

The substrates 11, 12, 13, 14, and 15 are composed of ceramic greensheets that are formed of dielectric ceramic materials by using, forexample, the doctor blade method or the Czochralski method, and arelaminated into the laminate body 16 and sintered.

Thus, in practice, in FIG. 1, a separating line does not appear betweenthe substrates 11, 12, 13, 14, and 15 in the direction in which thesesubstrates are laminated. The aforementioned external electrodes G, P₁,P₂, P₃, and P₄ may be formed after the laminate body 16 has beensintered.

A ground electrode 17 is provided on the major surface of the firstground electrode substrate 11. The size of the ground electrode 17 issuch that the ground electrode 17 completely covers the inner lineelectrode 21 a and the outer line electrode 22 a, which have a spiralshape and are provided on the dielectric substrate 12, excluding theperipheral region of the major surface of the first ground electrodesubstrate 11. The ground electrode 17 is connected to the externalelectrodes G, G for grounding through lead-out portions 17 a, 17 a.

The inner line electrode 21 a functioning as a main line and the outerline electrode 22 a functioning as a subordinate line are provided byprinting on the major surface of the dielectric substrate 12 at a stagein which the dielectric substrate 12 is a green sheet that has not beensintered. In the first preferred embodiment, the inner line electrode 21a and the outer line electrode 22 a preferably have substantially thesame width, and the respective numbers of turns of the inner lineelectrode 21 a and the outer line electrode 22 a are 2.5 and 1.5,respectively. The line length of each of the main and subordinate linesis less than a quarter of a wavelength.

The lead-out conductors 23 a, 24 a, and 25 a are provided on the majorsurface of the lead-out conductor substrate 13. The inner end of theinner line electrode 21 a having a spiral shape is connected to theexternal electrode P₁ for the main line through a via hole Vh₁ and thelead-out conductor 23 a, which are provided in the lead-out conductorsubstrate 13, and the outer end of the inner line electrode 21 a isconnected to the external electrode P₂ for the main line through a viahole Vh₂ and the lead-out conductor 24 a, which are provided in thelead-out conductor substrate 13.

The inner end of the outer line electrode 22 a having a spiral shape isconnected to the external electrode P₃ for the subordinate line througha via hole Vh₃ and the lead-out conductor 25 a, which are provided inthe lead-out conductor substrate 13, and the outer end of the outer lineelectrode 22 a is connected directly to the external electrode P₄ forthe subordinate line on the dielectric substrate 12.

A ground electrode 18 is provided on the major surface of the secondground electrode substrate 14 laminated on the lead-out conductorsubstrate 13. The size of the ground electrode 18 is such that theground electrode 18 completely covers the two line electrodes 21 a and22 a, which have a spiral shape and are provided on the dielectricsubstrate 12, excluding the peripheral region of the major surface ofthe second ground electrode substrate 14. The ground electrode 18 isconnected to the external electrodes G for grounding through lead-outportions 18 a. The ground electrode 18 is covered with the protectionsubstrate 15 which is laminated on the second ground electrode substrate14.

In the directional coupler 10 a having the aforementioned structure, theouter line electrode 22 a having a spiral shape and the inner lineelectrode 21 a having a spiral shape are coupled by side-edge couplingtherebetween. The inner line electrode 21 a is surrounded by the outerline electrode 22 a and disposed inside the outer line electrode 22 a.An enclosed area between the inner line electrode 21 a and the outerline electrode 22 a is substantially the same as an enclosed areabetween the inner edge of the innermost circumferential of the outerline electrode 22 a and the outer edge of the outermost circumferentialof the inner line electrode 21 a. Thus, only certain sections of theinner line electrode 21 a oppose sections of the outer line electrode 22a in the first area. Moreover, since the inner line electrode 21 a andthe outer line electrode 22 a are formed by printing, the thickness ofeach line electrode is thin. Thus, the capacitance formed between theinner line electrode 21 a and the outer line electrode 22 a is small,and high isolation between these line electrodes can be achieved.

Moreover, in the directional coupler 10 a, the inner line electrode 21 aand the outer line electrode 22 a have a spiral shape. In FIG. 2, forexample, the corresponding currents are transmitted through parallelfront left sections of the inner line electrode 21 a and the outer lineelectrode 22 a in the same direction, as indicated by arrow A. Thus, theinductance values of the line electrodes 21 a and 22 a become high atsections of the inner line electrode 21 a and the outer line electrode22 a. Accordingly, inductive coupling between the inner line electrode21 a and the outer line electrode 22 a becomes strong and capacitivecoupling between the inner line electrode 21 a and the outer lineelectrode 22 a becomes weak. Moreover, the inductance values of theinner line electrode 21 a and the outer line electrode 22 a can bereadily adjusted so that the inductance values agree with each other byadjusting the respective numbers of turns of the inner line electrode 21a and the outer line electrode 22 a.

In the directional coupler 10 a, the inner line electrode 21 a and theouter line electrode 22 a have a spiral shape, and the correspondingcurrents are transmitted through the sections of the inner lineelectrode 21 a and the outer line electrode 22 a that are parallel andadjacent to each other in the same direction. Thus, a high inductancevalue can be achieved while the size of the directional coupler 10 a issmall. The length of each line electrode can be less than a quarter of awavelength, and the size of the directional coupler 10 a can be reduced.

In the aforementioned description of the directional coupler 10 a, theinner line electrode 21 a is the main line electrode and the outer lineelectrode 22 a is the subordinate line electrode. Even when the innerline electrode 21 a is the subordinate line and the outer line electrode22 a is the main line, the directional coupler 10 a can operate in thesame manner. The same applies to the remaining preferred embodiments,which are described below.

Second Preferred Embodiment

FIG. 3 shows a directional coupler 10 b according to a second preferredembodiment of the present invention. While the dielectric substrate 12is used in the directional coupler 10 a according to the first preferredembodiment, which was described with reference to FIGS. 1 and 2, whereinthe inner line electrode 21 a and the outer line electrode 22 apreferably have substantially the same width on the dielectric substrate12; a dielectric substrate 12 a is used in the directional coupler 10 b,an inner line electrode 21 b and an outer line electrode 22 b areprovided on the dielectric substrate 12 a so that the width of the innerline electrode 21 b is narrower than that of the outer line electrode 22b.

When the width of the inner line electrode 21 b is narrower, theinductance value of the inner line electrode 21 b is increased.Accordingly, the number of turns of the inner line electrode 21 b can bereduced. Thus, a directional coupler 10 b that is smaller than thedirectional coupler 10 a can be obtained.

In FIG. 3, the same reference letters and numerals as in FIG. 2 areassigned to the corresponding components, and duplicate descriptionthereof is omitted. The advantages achieved by the second preferredembodiment are basically the same as those achieved by the firstpreferred embodiment.

Third Preferred Embodiment

FIG. 4 shows a directional coupler according to a third preferredembodiment of the present invention. While the dielectric substrate 12is used in the directional coupler 10 a according to the first preferredembodiment, which was described with reference to FIGS. 1 and 2, whereinthe inner line electrode 21 a and the outer line electrode 22 apreferably have substantially the same width on the dielectric substrate12; dielectric substrates 32, 33, and 34 are used in the directionalcoupler 10 c. Three inner line electrode components 21 aa, 21 ab, and 21ac, into which the inner line electrode is divided, are respectivelyprovided on the dielectric substrates 32, 33, and 34; and two outer lineelectrode components 22 aa and 22 ab, into which the outer lineelectrode is divided, are respectively provided on the dielectricsubstrates 32 and 33. When this arrangement is utilized, the inner lineelectrode and the outer line electrode are formed as helical lines.

In FIG. 4, the same reference letters and numerals as in FIG. 2 areassigned to the corresponding components, and duplicate descriptionthereof is omitted.

One end of the inner line electrode component 21 aa is connected througha via hole Vh₁₁ in the dielectric substrate 32 to a lead-out conductor23 b on a lead-out conductor substrate 31 and the external electrode P₁for the main line. The other end of the inner line electrode component21 aa is connected through a via hole Vh₁₂ in the dielectric substrate33 to one end of the inner line electrode component 21 ab on thedielectric substrate 33.

The other end of the inner line electrode component 21 ab is connectedthrough a via hole Vh₁₃ in the dielectric substrate 34 to one end of theinner line electrode component 21 ac on the dielectric substrate 34. Theother end of the inner line electrode component 21 ac is connecteddirectly to the external electrode P₂ for the main line on thedielectric substrate 34.

On the other hand, one end of the outer line electrode component 22 aais connected directly to the external electrode P₃ for the subordinateline on the dielectric substrate 32. The other end of the outer lineelectrode component 22 aa is connected through a via hole Vh₁₄ in thedielectric substrate 33 to one end of the outer line electrode component22 ab on the dielectric substrate 33. The other end of the outer lineelectrode component 22 ab is connected directly to the externalelectrode P₄ for the subordinate line on the dielectric substrate 33.

Even when this arrangement is utilized, the same advantages as in thedirectional coupler 10 a, which was described with reference to FIGS. 1and 2, can be achieved. As is apparent from FIG. 4, the inner lineelectrode is divided into the three inner line electrode components 21aa, 21 ab, and 21 ac, and the outer line electrode is divided into thetwo outer line electrode components 22 aa and 22 ab. Thus, the number ofline electrode components per unit area that are on the dielectricsubstrates 32, 33, and 34 can be reduced, and the size of thedirectional coupler can be further reduced.

Fourth Preferred Embodiment

FIG. 5 shows a directional coupler 10 d according to a fourth preferredembodiment of the present invention. In the directional coupler 10 d,the inner line electrode is divided into three inner line electrodecomponents 21 aa, 21 ab, and 21 ac, and the outer line electrode isdivided into three outer line electrode components 22 aa, 22 ab, and 22ac, as in the directional coupler 10 c according to the third preferredembodiment, which was described with reference to FIG. 4. These lineelectrode components are provided on three dielectric substrates 57, 58,and 59. Capacitances are formed between the external electrodes P₁ to P₄for the main and subordinate lines and the external electrodes G forgrounding.

One end of the inner line electrode component 21 aa is connected througha via hole Vh₂₁ in the dielectric substrate 57 to a lead-out conductor23 c on a lead-out conductor substrate 56 and the external electrode P₁for the main line. The other end of the inner line electrode component21 aa is connected through a via hole Vh₂₂ in the dielectric substrate58 to one end of the inner line electrode component 21 ab on thedielectric substrate 58. The other end of the inner line electrodecomponent 21 ab is connected through a via hole Vh₂₃ in the dielectricsubstrate 59 to one end of the inner line electrode component 21 ac onthe dielectric substrate 59. The other end of the inner line electrodecomponent 21 ac is connected directly to the external electrode P₂ forthe main line on the dielectric substrate 59.

On the other hand, one end of the outer line electrode component 22 aais connected through a via hole Vh₂₄ in the dielectric substrate 57 to alead-out conductor 26 on the lead-out conductor substrate 56 and theexternal electrode P₄ for the subordinate line. The other end of theouter line electrode component 22 aa is connected through a via holeVh₂₅ in the dielectric substrate 58 to one end of the outer lineelectrode component 22 ab on the dielectric substrate 58. The other endof the outer line electrode component 22 ab is connected through a viahole Vh₂₆ in the dielectric substrate 59 to one end of the outer lineelectrode component 22 ac on the dielectric substrate 59. The other endof the outer line electrode component 22 ac is connected directly to theexternal electrode P₃ for the subordinate line on the dielectricsubstrate 59.

A dummy substrate 55 a is laminated between the lead-out conductorsubstrate 56 and the ground electrode substrate 11, and a dummysubstrate 55 b is laminated between the dielectric substrate 59 and theground electrode substrate 14. In the directional coupler 10 d,capacitor electrode substrates 51 to 54 for forming capacitances arelaminated, in this order from the bottom, under the ground electrodesubstrate 11.

A capacitor electrode 61 is provided on the major surface of thecapacitor electrode substrate 51. The capacitor electrode 61 is arrangedso that the capacitor electrode 61 covers a substantially entire area ofthe major surface of the capacitor electrode substrate 51, excluding theperipheral region of the major surface of the capacitor electrodesubstrate 51. The capacitor electrode 61 is connected to the externalelectrodes G, G for grounding through lead-out portions 61 a, 61 a. Twostrip-shaped capacitor electrodes 63 b and 64 b are provided on themajor surface of the capacitor electrode substrate 52. The capacitorelectrodes 63 b and 64 b are connected to the external electrodes P₄ andP₃ for the subordinate line, respectively.

A capacitor electrode 62 is provided on the major surface of thecapacitor electrode substrate 53. The capacitor electrode 62 is arrangedso that the capacitor electrode 62 covers substantially the entire areaof the major surface of the capacitor electrode substrate 53, excludingthe peripheral region of the major surface of the capacitor electrodesubstrate 53. The capacitor electrode 62 is connected to the externalelectrodes G, G for grounding through lead-out portions 62 a, 62 a. Twostrip-shaped capacitor electrodes 63 a and 64 a are provided on themajor surface of the capacitor electrode substrate 54. The capacitorelectrodes 63 a and 64 a are connected to the external electrodes P₁ andP₂ for the main line, respectively.

The advantages achieved by the fourth preferred embodiment are the sameas those achieved by the first preferred embodiment. Moreover, when theaforementioned arrangement is utilized, capacitances are formed betweenthe capacitor electrodes 63 a and 64 a, the capacitor electrode 62, andthe ground electrode 17; and between the capacitor electrodes 63 b and64 b, the capacitor electrode 61, and the capacitor electrode 62. Due tothe functions of these capacitances, the resonant frequencies of theinner line electrode, which is divided into the three inner lineelectrode components 21 aa, 21 ab, and 21 ac, and the outer lineelectrode, which is divided into the three outer line electrodecomponents 22 aa, 22 ab, and 22 ac, can be reduced. Thus, the size ofthe directional coupler 10 d can be further reduced by shortening thelengths of the line electrodes to obtain a predetermined resonantfrequency.

Other Preferred Embodiments

Directional couplers according to the present invention are not limitedto the aforementioned preferred embodiments and can have variousstructures within the gist and scope of the present invention.

For example, in the directional coupler 10 a, although not specificallyshown in the drawings, the inner line electrode 21 a may be provided onone dielectric substrate, and the outer line electrode 22 a may beprovided on another dielectric substrate. In this arrangement, thecapacitance between the inner line electrode 21 a and the outer lineelectrode 22 a can be reduced, resulting in high isolation between theseline electrodes.

The present invention may be applied to directional couplers for amicrowave band as described above, and in particular, is excellent inthat a high coupling value and high isolation characteristics can beachieved.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A directional coupler comprising: a first dielectric layer; a seconddielectric layer; and two line electrodes arranged on each of the firstand second dielectric layers; wherein the two line electrodes include aninner line electrode and an outer line electrode that surrounds theinner line electrode, as viewed from above, such that only some sectionsof the inner line electrode oppose some sections of the outer lineelectrode and remaining sections of the inner line electrode do notoppose remaining sections of the outer line electrode; a first end ofthe inner line electrode arranged on the first dielectric layer and afirst end of the inner line electrode arranged on the second dielectriclayer are connected through a first via hole in the first dielectriclayer; a first end of the outer line electrode arranged on the firstdielectric layer and a first end of the outer line electrode arranged onthe second dielectric layer are connected through a second via hole inthe first dielectric layer; and corresponding currents are transmittedin the same direction through sections of the inner line electrode andthe outer line electrode that are adjacent and substantially parallel toeach other.
 2. A directional coupler comprising: a first dielectriclayer; a second dielectric layer; and two line electrodes arranged oneach of the first and second dielectric layers; wherein the two lineelectrodes include a spiral-shaped or helical-shaped inner lineelectrode and a spiral-shaped or helical-shaped outer line electrodethat surrounds the inner line electrode, as viewed from above, such thatonly some sections of the inner line electrode oppose some sections ofthe outer line electrode and remaining sections of the inner lineelectrode do not oppose remaining sections of the outer line electrode;a first end of the inner line electrode arranged on the first dielectriclayer and a first end of the inner line electrode arranged on the seconddielectric layer are connected through a first via hole in the firstdielectric layer; and a first end of the outer line electrode arrangedon the first dielectric layer and a first end of the outer lineelectrode arranged on the second dielectric layer are connected througha second via hole in the first dielectric layer.
 3. The directionalcoupler according to claim 1, further comprising a third dielectriclayer and an inner line electrode arranged on the third dielectriclayer, wherein a second end of the inner line electrode arranged on thefirst dielectric layer and a first end of the inner line electrodearranged on the third dielectric layer are connected through a third viahole in the third dielectric layer.
 4. The directional coupler accordingto claim 1, wherein a length of each of the inner line electrode and theouter line electrode is less than a quarter of a wavelength.
 5. Thedirectional coupler according to claim 1, wherein a width of the innerline electrode is smaller than a width of the outer line electrode. 6.The directional coupler according to claim 1, wherein a number of turnsof the inner line electrode is larger than a number of turns of theouter line electrode.
 7. The directional coupler according to claim 1,wherein the inner line electrode and the outer line electrode arearranged on the same plane.
 8. The directional coupler according toclaim 1, wherein the inner line electrode and the outer line electrodeare arranged on different planes.
 9. The directional coupler accordingto claim 1, wherein at least one of the inner line electrode and theouter line electrode is divided into line electrode components arrangedon a plurality of planes, and the divided line electrode components areconnected in series with each other through the first or the second viahole.
 10. The directional coupler according to claim 1, furthercomprising a fourth dielectric layer and a ground electrode arranged onthe fourth dielectric layer, wherein a capacitance is formed between theground electrode and ends of the inner line electrode and the outer lineelectrode.
 11. The directional coupler according to claim 2, furthercomprising a third dielectric layer and an inner line electrode arrangedon the third dielectric layer, wherein a second end of the inner lineelectrode arranged on the first dielectric layer and a first end of theinner line electrode arranged on the third dielectric layer areconnected through a third via hole in the third dielectric layer. 12.The directional coupler according to claim 2, wherein a length of eachof the inner line electrode and the outer line electrode is less than aquarter of a wavelength.
 13. The directional coupler according to claim2, wherein a width of the inner line electrode is smaller than a widthof the outer line electrode.
 14. The directional coupler according toclaim 2, wherein a number of turns of the inner line electrode is largerthan a number of turns of the outer line electrode.
 15. The directionalcoupler according to claim 2, wherein the inner line electrode and theouter line electrode are arranged on the same plane.
 16. The directionalcoupler according to claim 2, wherein the inner line electrode and theouter line electrode are arranged on different planes.
 17. Thedirectional coupler according to claim 2, wherein at least one of theinner line electrode and the outer line electrode is divided into lineelectrode components arranged on a plurality of planes, and the dividedline electrode components are connected in series with each otherthrough the first or the second via hole.
 18. The directional coupleraccording to claim 2, further comprising a fourth dielectric layer and aground electrode arranged on the fourth dielectric layer, wherein acapacitance is formed between the ground electrode and ends of the innerline electrode and the outer line electrode.